Flowmeters are used to determine the mass flow rate of a fluid flowing through a tube. Coriolis mass flowmeters use the vibration pattern of two measuring tubes arranged in parallel for this purpose. An electro-dynamical driving system is normally used to excite the measuring tubes at one of their resonance frequencies. Sensors, usually also electro-dynamical sensors, measure the vibration of the measuring tubes. Typically, at least two pairs of sensors distributed over the length of the measuring tubes are used for this purpose. The measuring tubes may be straight tubes, such as disclosed in U.S. Pat. No. 5,602,345 A, loop-like tubes, as described in U.S. Pat. No. 4,781,069 A, or U-shaped measuring tubes, such as disclosed in U.S. Pat. No. 5,301,557 A, U.S. Pat. No. 8,931,354 A or U.S. Pat. No. 9,194,731 B2. The measuring tubes are solidly mounted on a support at their inlet and outlet ends. During use, the measuring tubes are oscillated about axes which are located adjacent to the solid mounting points. So-called node plates are often fixed in the region of these axes in order to additionally stabilize the measuring tubes and to make sure that the generated Coriolis forces in the measuring tubes are substantially linear spring forces. At the ends of the measuring tubes a flow divider and, respectively, a flow combiner are attached so that the flowmeter can be mounted to an inlet and an outlet pipe.
The assembly comprising the measuring tubes, supports, flow divider and flow combiner, carriers for the sensors and the driver units and optional node plates is often referred to as the tuning fork of a flowmeter. The components of the tuning fork are normally fixed to each other by high-temperature brazing. It is crucial during the brazing steps that the components of the tuning fork are exactly fixed and held in their correct positions in order to avoid any deformation due to thermal expansion and contraction during the brazing process. Complicated and expensive brazing tools are generally used for this purpose. The brazing tool has to be exactly adapted to the specific tuning fork and can normally not be used for any other type of tuning fork. The brazing tool is slightly deformed and worn off with each use and degrades so that it can be used only a limited number of times. This makes the brazing process and the production of the tuning fork rather expensive. Even if the brazing tool is formed of a material with a very high thermal stability this does not really solve the problems. First of all, the brazing tool is more expensive and, second, has the additional disadvantage that its coefficient of thermal expansion does not match with the materials used for the components of the tuning fork. As a result, deformations of the tuning fork components during brazing are experienced.